An arrangement for amplifying an output signal of a MEMS capacitive sensor comprises the MEMS capacitive sensor and a signal processing circuit coupled to the MEMS capacitive sensor. The MEMS capacitive sensor may be configured as a MEMS microphone. The signal processing circuit is configured to provide a bias voltage for operating the MEMS capacitive sensor and to amplify the output signal of the MEMS capacitive sensor and to provide an amplified output signal. The bias voltage is used to bias a capacitor of the MEMS capacitive sensor having a variable capacitance.
The signal processing circuit, which may be configured as an ASIC signal processing circuit, may comprise an amplifier, for example, an inverting amplifier, a positive/negative bias voltage generator, for example, a bias voltage pump, to provide the bias voltage for the MEMS capacitive sensor and a large AC coupling capacitance being arranged in a signal path between an input terminal of the signal processing circuit coupled to an output terminal of the MEMS capacitive sensor to receive the output signal of the MEMS capacitive sensor and an amplifier to amplify the received output signal of the MEMS capacitive sensor.
The output signal provided at the output terminal of the MEMS capacitive sensor and received at the input terminal of the signal processing circuit may be taken from a backplate of the capacitor of the MEMS capacitive sensor. The backplate of the capacitor may be the side with the smallest parasitic capacitance. A membrane of the capacitor of the MEMS capacitive sensor may be connected to a “reference ground” of the amplifier of the signal processing circuit.
In a standard CMOS process, the AC coupling capacitance causes a certain loss of the signal from the backplate of the capacitor of the MEMS capacitive sensor because of an unavoidable parasitic capacitance between the backplate of the capacitor of the MEMS capacitive sensor and the bulk substrate of the signal processing circuit. One could use advanced (or expensive) processes which offer MiM capacitors options. In this case, the parasitic portion can be only a few percent, for example, 2%, of the capacitance value of the coupling capacitance. However, the parasitic effects deteriorate the output signal of the MEMS capacitive sensor received by the signal processing circuit, and, as a consequence, the SNR (signal to noise ratio) of the MEMS capacitive sensor, for example, the MEMS microphone is further worsened.
It is desired to provide a MEMS capacitive sensor that may be coupled to a signal processing circuit to provide a supply and bias voltage for the MEMS capacitive sensor and to amplify the output signal of the MEMS capacitive sensor, wherein the influence of parasitic effects to the amplification process of the output signal of the MEMS capacitive sensor is reduced. Furthermore, there is a desire to provide an arrangement for amplifying an output signal of a MEMS capacitive sensor, wherein the influence of parasitic effects to the amplification process of the output signal of the MEMS capacitive sensor is reduced.